Hermetically sealed pump

ABSTRACT

A hermetically sealed pump includes a cylinder that defines a piston chamber for a reciprocating piston driven through an eccentric cam member and a cam follower operatively connected between the piston and the cam. A fluid manifold is associated with the piston cylinder and has suction and discharge ports located in communication with the piston chamber for supplying fluid to and discharging fluid from that chamber, and a pair of valves are operatively associated with these ports for simultaneously opening one of the ports and closing the other of the ports, in response to pressure in the piston chamber. A toroidally shaped rolling diaphragm hermetically seals the piston chamber on the side of the piston opposite the ports, thereby to prevent loss of fluid in the pump through the piston chamber.

Malcoslty [451 May 7,1974

1 1 HERMETICALLY SEALED PUMP [75] Inventor: Norman D. Malcosky, Columbus,

Ohio

[73] Assignee: Columbia Gas System Service Corporation, Wilmington, Del.

[22] Filed: Dec. 11, 1972 [21] Appl. No.: 313,756

[52] US. Cl 417/439, 92/98 R, 417/571, 417/902 [51] lnt. Cl. F041) 21/02, F04b 39/00 [58] Field of Search 417/571, 439, 902, 413; 92/98 D, 98 R, 165

[56] References Cited 7 UNITED STATES PATENTS 2,019,747 12/1931 Taylor 417/571 X 2,826,153 3/1958 Johnson 417/571 X 3,421,732 1/1969 Golden 92/98 R X 3,473,726 10/1969 Bachmann 417/571 X FOREIGN PATENTS OR APPLICATIONS 1,126,864 7/1956 France 417/571 Primary Examiner-Car1ton R. Croyle ljssistant ExaminerRichard E. Gluck Attorney, Agent. or Firm- Harold L. Stults, Curtis, Morris & Safford 5 7 ABSTRACT A hermetically sealed pump includes a cylinder that defines a piston chamber for a reciprocating piston driven through an eccentric cam member and a cam follower operatively connected between the piston and the cam. A fluid manifold is associated with the piston cylinder and has suction and discharge ports located in communication with the piston chamber for supplying fluid to and discharging fluid from that chamber, and a pair of valves are operatively associated with these ports for simultaneously opening one of the ports and closing the other of the ports, in response to pressure in the piston chamber. A toroidally shaped rolling diaphragm hermetically seals the piston chamber on the side of the piston opposite the ports, thereby to prevent loss of fluid in the pump through the piston chamber.

15 Claims, 6 Drawing Figures PATENTEHMAY 7 m4 3.809.506

sum 1 OF 2 IO 28 60 I00 92 I HERMETICALLY SEALED PUMP The present invention relates to a fluid pump and in particular to a pump for liquids which must be pumped at high pressure differentials and low flow rates.

There presently is a demand for high quality precision liquid pumps which are adapted to be utilized in airconditioning systems wherein high pressure differentials and low flow rates are required. Such pumps are extremely important in airconditioning systems of the absorption type and preferably must be hermetically sealed to eliminate the possibility of loss of the refrigerant fluids during the pumping cycle.

Accordingly, it is an object of the present invention to pump liquids at high pressure differentials and low flow rates by an efficient hermetically sealed pump.

I Yet another object of the present invention is to provide a fluid or liquid pump which is hermetically sealed and adapted to pump liquids at high pressure differentials and low flow rates.

Yet another object of the present invention is to provide a pump of the character described which is relatively inexpensive to manufacture, simple and durable in operation.

In accordance with an aspect of the present invention a hermetically sealed pump is provided for use in absorption type refrigeration systems wherein it is desired to pump liquids, such as the refrigerant solution, at high pressure differentials and at low flow rates. The pump preferably is provided with an electric motor having a rotary power output shaft on which an eccentric rotary cam surface is provided for driving a piston assembly operatively associated with the motor.

The piston assembly includes a piston cylinder having a piston chamber formed therein, in which a piston is located for reciprocation through a piston rod and cam follower from the rotary cam element. The piston rod is guided in a guide flange which is operatively connected to the piston cylinder, between the cylinder and the cam, and has a central bore opening towards the piston and piston chamber, through which the piston rod extends. A compression spring operatively connected between the flange and the cam follower biases the cam follower into engagement with the cam so that the piston is reciprocated during rotation of the cam by the electric motor, thereby to alternately produce relatively low and high pressures in th cylinder.

A fluid manifold is located on the opposite side of the piston cylinder from the guide flange. This manifold has independent fluid inlet and outlet ports formed therein for separate communication with the piston chamber. A flap valve is operatively associated with the inlet port for opening that port and permitting fluid to flow into the piston during the downward or suction stroke of the piston, i.e., when there is low pressure in the chamber, while closing the inlet port on the upward or discharge stroke of the piston, i.e., when there is high pressure in the chamber. On the other hand, a check valve is operatively associated with the outlet port for closing the outlet port on the downward suction stroke of the piston and opening the outlet port on the upward discharge stroke of the piston, thereby assuring efficient pumping operation.

Finally, the pump is hermetically sealed by a generally toroidally shaped diaphragm formed of an elastomeric material and operatively connected between the cylinder and the piston on the side of the piston opposite the manifold. The diaphragm is of the rolling type and prevents loss of fluid from the piston cylinder during the pumping operation. I

The above, and other objects, features and advantages of this invention, will be apparent in the following detailed description of an illustrative embodiment thereof which is to be read in connection with the accompanying drawings, wherein:

FIG. 1 is a side view, with parts broken away and parts in section, of a hermetically sealed liquid pump constructed in accordance with one embodiment of the present invention;

FIG. 2 is a top view of the pump illustrated in FIG.

FIG. 3 is an enlarged schematic sectional view of the piston assembly during its downward suction stroke;

FIG. 4 is a sectional view similar to FIG. 3 showing the piston assembly during its upward discharge stroke;

FIG. 5 is a view taken along line 5-5 of FIG. 3 showing the relationship of the valves of the piston assembly; and

FIG. 6 is a schematic illustration of another embodiment of the present invention.

Referring now to the drawing in detail and initially to FIG. 1 thereof, it will be seen that a pump 10, constructed in accordance with the present invention, includes an electric motor 12 having a shell 14 in which a cylindrical core 16 and central shaft 18 are rotatably mounted. Motor 12 also includes a coil 20 which, in the conventional manner, causes rotation of core 16 and shaft 18. The latter has a motor cooling fan blade 19 rigidly mounted thereon and is utilized to drive a piston assembly 22 which includes a manifold 24 having a threaded inlet port 26 and a threaded outlet port 28. Upon operation of motor 12, shaft 18 operates the piston assembly 22, as more fully described hereinafter, in

order to draw liquid through the inlet 26, into the pis ton assembly, the outlet 28.

In the illustrative embodiment of the present invention, motor shaft 18 includes a threaded end portion 30 and thence discharge the liquid through on which a cam bushing 32 is threadedly secured. Cam' bushing 32 includes a central cam portion 34 whose axis of rotation is slightly offset from the central axis of rotation 36 of shaft 18 and the remainder of bushing 32 so that the outer peripheral surface 38 of the cam bushing moves in an eccentric path about the axis of rotation of shaft 18. Surface 38 thereby defines a cam surface for operating piston assembly 22.

Cam bushing 32 also includes an inner portion 40 whose peripheral surface is substantially coaxial with that of shaft 18, so that the shaft and the cam bushing can berotatably mounted in bearing 41 seated in the front cover plate 42 of housing 12. It is only that portion 34 of cam bushing 32, located exteriorly of cover 42, which has the eccentricity described above.

A bearing 44 is secured on eccentric surface 38 in order to drive piston assembly 22, as described hereinafter. This bearing is retained on member 32 between a snap ring 46 and a shoulder 48 milled in the cam bushing. Beyond snap ring 46, cam bushing 32 includes an elongated shaft portion 50 which may be used to transmit power to other devices, as for example, pumps, fans, or the like, through a conventional gear or pulley arrangement. Of course, extension 50 is formed to be coaxial with shaft 18 so that no eccentricities re- 3, sult during the use thereof in driving any other equipment.

, Piston assembly 22 (FIGS. 3 and 4) includes a piston cylinder 52 secured to cover plate 42 of housing 14 in any convenient manner. Cylinder 52 includes an interior chamber 54 defined by an axial piston bore 56 formed therein. Thus, chamber 54 defines a piston chamber in which a piston 58 is positioned for reciprocation by the eccentrically rotated bearing 44.

Manifold 24 is operatively secured to cylinder 52 with a valve plate 60 secured therebetween. The manifold, as mentioned above, includes an inlet port 26, through which fluid passes to the piston assembly 22, and an outlet port 28, through which fluid is discharged from the piston assembly during operation of the device. lnlet port 26 is in communication with a suction port 61 formed in the valve plate 60, whereby communication is provided between the inlet port and chamber 54. Similarly, valve plate 60 includes an outlet port 62 which provides communication between piston chamber 54 and outlet 28, for discharge of fluid drawn into the piston chamber.

During operation of the piston assembly, piston 58 reciprocates between a top dead center position and a bottom dead center position, illustrated respectively in FIGS. 4 and 3. As the piston moves downwardly towards its bottom dead center position, it increases the volume within piston chamber 54, thereby decreasing the pressure therein. As a result of this decrease in pressure, the pressure of liquid in the inlet port forces open a valve mechanism 63 to permit fluid to enter the piston chamber. Valve mechanism 63 comprises a flap valve 64 located between valve plate 60 and cylinder 52. Flap valve 54 includes a main body portion 65, illustrated most clearly in FIG. 5, having an aperture 66 therein which is generally complementary to the area of piston chamber 54. The main body of flap valve 64 includes an elongated extension 68 which extends across opening 66, and has an enlarged head portion 70 positioned to cover inlet port 61' in valve plate 60. Flap valve 64 is formed of a flexible plastic, or metal, material so that the extension 68 can flex under variations in pressure between the piston chamber and the inlet port. Thus, as piston 58 moves in its downward or suction stroke, the pressure in chamber 54 decreases and the pressure in inlet port 26 causes extension 68 to move downwardly, away from port 61, thereby permitting liquid to enter piston chamber 54. On the other hand, in the upward pressure stroke of piston 58, i.e.,

towards its top dead center position, the pressure within chamber 54 increases above that in the inlet line 26 so that the enlarged portion 70 of extension 68 is moved back into engagement against the lower surface of valve plate 60, thereby to close port 63 and prevent liquid flow from chamber 54.

During the upward stroke of piston 58, fluid pressure within piston chamber 54 is increased and thus fluid is discharged through outlet port 62 in valve plate 60. However, a check valve 72 is located in complementary bores 74, 76 formed respectively in discharge port 62 and outlet port 28. This check valve includes an outer cylindrical body 78 which includes a valve seat 80 therein. A valve disk 82 of conventional construction is located within valve body'78 and is biased towards a closed position, illustrated in FIG. 3, by a spring 84. Thus, upon the downward stroke of piston 58, spring 84 holds valve disk 82 against seat 80 to prevent liquid in port 28 from flowing backwardly into chamber 54., On the other hand, during the upward pressure stroke of piston 58, the increasing pressure of the fluid within chamber 54 ultimately overcomes the bias of spring 84, thereby to move disk 82 against spring 84 and permit the pressurized fluid within chamber 54 to discharge through discharge port 62 and outlet port 28. Accordingly, it is seen that during the operation of the device, one or the other of the valves 64, 72 is open and that these valve assemblies are responsive to pressure within piston chamber 54, so as to automatically meter fluid into and out of the piston cylinder.

Piston 58 is mounted on a piston rod having a free end 92 which is connected through a dowel rod (or in any convenient manner) to a cam follower or shoe 96. The latter is engaged against the surface 98 of bearing 44 so as to be reciprocated by the bearing during its eccentric rotation with cam bushing section 38. Piston rod 92 is guided during this reciprocation in an annular guide flange 100 which is secured in any convenient manner to piston cylinder 52. Flange 100 includes an inner bore 102 which opens towards piston 58 and piston chamber 54 and which is in axial alignment with an auxiliary guide bore 104. A guide bushing 106 is located in bore 104 and engages piston rod 90 to assure low friction sliding of the piston rod in the guide flange.

Guide flange 100 also provides a mounting for a compression spring 108 which surrounds the portion of flange 100 forming guide bore 104. One end of spring 108 is engaged against flange 100 and the opposite end thereof is engaged against a spring retainer 106 secured to the free end of piston rod 92. In this manner, spring 108 biases cam follower 96 against the surface of bearing 44 to assure positive contact therebetween at all times so that cam shoe 94 always follows the eccentrically rotating bearing. In this manner piston 58 is automatically and positively returned to its bottom dead center position.

Piston assembly 22 is hermetically sealed to prevent loss of liquid or gas from the piston chamber through the lower side thereof by a rolling diaphragm assembly 110. This assembly includes a generally toroidally shaped diaphragm 112 formed of an elastomeric material. Diaphragm 112 has an outer edge 114 which is clamped between flange 100 and cylinder 52, as most clearly seen in FIGS. 3 and 4, and an inner edge 116 which is similarly clamped'between piston 58 and an enlarged, generally circular guide disk 118 formed integrally with piston rod 90.

Diaphragm 112 can be squeezed between the various parts, in the manner illustrated in FIGS. .3 and 4, and held therebetween by frictional engagement with the parts, or it may be otherwise secured in position in any convenient manner. In any case, the diaphragm is held tightly in the position illustrated so that the edges thereof are slightly compressed, causing the central portion of the diaphragm to bulge, and thereby form a curved surface 120 along its lower side.

Preferably, flange 100 and guide 118 are provided with curved edge portions 112, 124, respectively, located adjacent the curved surface 120 of diaphragm 112, thereby to support the diaphragm during rolling movement. As seen in the drawing, curved surface 122 of flange 100 is formed along the top edge of bore 102 and curved surface 124 of guide disk 118 is formed along the top edge of its peripheral annular wall. It is noted that diaphragm 112 is formed of a relatively thick layer of material, so that the diaphragm will have the capacity for a wide range of movement and can enter the space between surfaces 122, 124. The large range of movement permits the pump to withstand higher pressures as the diaphragm moves further down into the space between the surfaces 122, 124 under increasing pressures but is continuously supported by these surfaces to resist such pressures.

Piston 58, and piston rod 90, are dimensioned so that at the top dead center of the pistons stroke, curved surface 124 of guide disk 118 is located at a slightly higher level than guide surface 122, as seen in FIG. 4, while at its bottom dead center position, guide surface 124 is located at a slightly lower level than surface 122 (FIG. 3). As a result, during movement between top dead center and bottom dead center, the rolling diaphragm rolls along surfaces 122, 124 in opposite directions. That is, for'example, as illustrated in FIG. 4, diaphragm 112, at the top dead center of piston 58, contacts rolling surface 122 at point A, while contacting the curved surface 124 at a point B (FIG. 4). As piston 58 moves downwardly the point of contact between diaphragm 112 and surface 122 moves downwardly to the point A (FIG. 3) whereas thepoint of contact between the diaphragm and the guide surface 124 moves upwardly to the point B (FIG. 3). Thus, these points of contact move in the opposite direction, thereby defining contact zones (A and B respectively) on surfaces 122, 124 at which the rolling diaphragm is continuously supported during operation of the device. (It is noted that for clarity, zones A" and B have been stipled in the drawing.) This rolling support improves the sealing characteristics of the diaphragm and its useful life.

Any pressure increase in chamber 127 above diaphragm 112, i.e., between piston 58 and the diaphragm, will cause the zones of contact with the surfaces 122 and 124 to move downwardly. On the other hand, any decrease in pressure in the area above the diaphragm will cause those zones of contact to move upwardly. The diaphragm is constructed of sufficient thickness to allow this movement without effecting the generally toroidal shape of the elastomeric material. In any case, because of the construction of the invention, the diaphragm will always be in contact with and supported by the curved surfaces 122, 124 during operation of the device, irrespective of the pressure above the diaphragm. In this regard, it is noted that the diaphragm is important in hermetically sealing the piston in that it is possible that during operation of the device, some liquid or gas'can escape past the piston rings 126 of piston 58 into chamber 127above the diaphragm. In previously proposed devices, these gases or liquids would simply leak out, causing damage and also decreasing the supply of refrigerant fluid in the airconditioning system in which the pump is utilized. With the present invention, on the other hand, the fluid remains in the system, flowing through conduit 128 to the pump inlet 26, and thus is contained in the system. Conduit 128 provides communication between chamber 127 and inlet port 26, thereby assuring that the diaphragm 112 is not subjected to varying and excessive pressures, but rather only to the inlet fluid pressure. This extends the useful life of the diaphragm. It is noted that the diaphragm construction and mounting is such that the volelectric motor 12 causes rotation of eccentric cam bushing 32. As a result, the eccentric section 38 thereof causes eccentric rotation of the bearing 44. By engagement of cam follower 96 against the surface of bearing 44, piston 58 is reciprocated within piston chamber 54. As a result, on the downward-suction strokeof the piston, liquid or fluid to be pumped is drawn in through inlet port 26 and passes through suction port 63 and the now open flap valve 64 to piston chamber 54. On the upward stroke of piston 58, the flap valve 64 automatically closes and the bias of spring 84 in check valve 74 is overcome, so as to permit the pressurized liquid to be discharged through the outlet 28. Loss of fluid of course is prevented by the hermetic seal arrangement provided by rolling diaphragm 112, clamped between the flange 100, cylinder 52, piston 58 and guide disk 118.

In another embodiment of the present invention, illustrated in FIG. 6 of the drawings, more than one piston assembly 22 can be utilized with the motor 12. As shown therein, two piston assemblies 22 are operatively connected on opposite sides of eccentric bearing 44. In this case springs 108 operate in the same manner as described above to hold shoes 96 of the piston rods against the cam bearing. As a result, piston assemblies 22 are operating in opposite phases to draw fluid from inlet supply 125 to theri respective inlet ports. In this manner, the capacity of th pump is substantially double that of the embodiment of FIGS. 1 to 5. Of course, other piston assemblies may also be mounted on pump 10, in a similar manner, as would be understood by those skilled in the art, to further increase the capacity of the entire pump arrangement.

Accordingly, it is seen that a relatively simple and inexpensive pumping mechanism is disclosed which provides accurate pumping at high pressure differentials and low flow rates. The pumping assembly is hermetically sealed, because of the elastomeric rolling diaphragm sealing arrangement described above. This seal has a relatively long life and prevents leakage from the piston assembly. In addition, the spring biased piston arrangement utilized in the present invention guarantees that the cam follower on the piston rod remains in contact with the cam drive mechanism in order to retract the piston to its bottom dead center position, thereby to produce suction in the piston chamber 54 and draw liquid into the chamber for pressurization and discharge through outlet port 28.

Although illustrative embodiments of the present invention have been described herein with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments and that various changes and modifications may be effected therein by one skilled in the art without departing from the scope or spirit of this invention.

What is claimed is:

1. A pump comprising, a cylinder defining a piston chamber, a piston located in said cylinder for reciprocation therein, a fluid manifold associated with said piston cylinder and having suction and discharge ports located in communication with said piston chamber, valve means operatively associated with said ports for simultaneously opening one of said ports and closing the other of said ports in responseto the pressure in said piston chamber, means for hermetically sealing said piston chamber on'the side of said piston opposite said ports, thereby. to prevent loss of fluid in said pump through said piston chamber, and means for reciprocating said piston including a driven eccentric cam and a cam follower operatively connected between said pistonand said cam, and means biasing said cam follower into engagement with said cam whereby rotation of said eccentric cam causes reciprocation of said piston in said chamber to alternately produce relatively low and high pressuresin said chamber, thereby to draw fluid from said manifo ld through said suction port into said piston chamber and thence discharge said fluid through said discharge port; said means forhermetically sealing said piston chamber comprising a diaphragmformed of an elastomeric material operatively connected between said cylinder and said piston and having a first side facing said piston chamber and a second side opposite said first side and remote from said piston chamber; said diaphragm having inner and outer edge portions respectively connected to said piston and said cylinder and .having'a thickness between said inner and outer edge portions which is greater than the thickness ofsaid edge portions thereby to form a bulge in said diaphragm between said edge portions to define a pairof-curved rolling surfaces thereon; and means forming a pair of opposed continuously curved surfaces adjacent said second side of said diaphragm in predetermined relation to each other whereby said curved rollingsurface's of the'diaphragm roll along said opposed continuously curved surfaces in opposite-directions during reciprocation of said piston.

. 2. A pump as defined in claim 1 wherein said piston includes a piston rodconnected to said follower, and said means forming said opposed continuously curved surfaces includes a guide'flange having a central bore opening towards said piston and piston chamber, said flangehaving a peripheral edge portion surrounding said bore, said edge portion being rounded to form one of said continuously curved surfaces, and a generally disk shapedjg'uide member on said piston rod having a peripheral -rounded surface forming the other of said continuously curved surfaces.

I 3.- A pump'as defined in claim 2 .wherein said diaphragm has a generally toroidal configuration when viewed'in plan, said outer'edge portion being clamped between said guide flange and said cylinder and said inner edge portion being clamped between said piston and said guide member thereby to form said bulge in said diaphragm between said inner and outer edge portions and form said curved rolling surfaces engaging the continuously curved surfaces of said flange and guide member.

4. A pump as defined in claim 3 wherein said guide member is positioned to have its curved surface located at a level above the curved surface of said flange when said piston is in its top dead center position and at a level below the curved surface of said flange when said piston is in its bottom dead center position.

5'. A pump as defined in claim 2 wherein said means for biasing said cam follower into engagement with said cam comprises a compression spring operatively connected between said flange and said cam follower.

, 6. A pump as defined in claim 2 wherein said .valve means includes a flap valve operatively associated with said suction port. v

7. A pump as defined in claim 6 wherein said valve means further includes a check valve operatively associated with said discharge port for opening said discharge port when said flap valve closes said suction port.

8 A pump as defined in claim 7 including an electric motor having an output shaft, and said eccentric cam comprises an eccentric cam bushing secured to said shaft and a rotary bearing mounted on said cam bushing in engagement with said cam follower.

9. A pump as defined in claim 1 wherein said diaphragm cooperates with said piston to form a fluid chamber therebetween in said cylinder, and said cylinder has a fluid passage formed therein providing fluid communication between said fluidchamber and said suction port.

10. The pump as defined in claim 3 wherein said continuously curved surfaces are spaced from each other and the bulge in said diaphragm enters the space between said continuously curved spaces thereby allowing said pump to withstand high pressures.

11. A pump comprising, an electric motor having a rotary power output shaft, means forming an eccentric rotary cam surface mounted on said shaft, and a piston assembly operatively associated with said eccentric cam surface including a piston cylinder having a piston chamber formed therein, a piston located in said cylinder, having a piston rod and an operatively associated cam follower, a guide flange operatively connected to I I said cylinder between said cylinder and said cam and having a central bore opening towards said piston and piston chamber, said piston rod extending through said bore and being guided thereby during reciprocation of said piston, a compression spring operatively connected between said flange and said cam follower for biasing said cam follower into engagement with said cam surface whereby said piston is reciprocated during rotation of said cam surface to alternately produce relative low and high pressures in said cylinder, a fluid manifold operatively associated with said cylinderand having independent fluid inlet and outlet ports formed therein, anc communicating with said piston chamber, first valve means operatively associated with said inlet port for opening said inlet port and permitting fluid to flow into said piston chamber during the downward suction stroke of said piston and closing said inlet port on the upward-discharge stroke of said piston, and second valve means operatively associated with said outlet port for closing said outlet port on the downwardsuction stroke of said piston, and opening said outlet port on the upward-discharge stroke of said piston, and a generally toroidally-shaped diaphragm formed of an elastomeric material operatively connected between said cylinder and said piston for hermetically sealing said piston chamber to prevent loss of fluid therefrom during operation of said pump; said diaphragm having a first side facing said piston chamber, a second side opposite said first side and remote from said piston chamber, inner and outer edge portions respectively connected to said piston and said cylinder, and a thickness between said inner and outer edge portions which is greater than the thickness of said edge portions,

thereon: said flange bore having a rounded upper peripheral edge portion adjacent said cylinder defining a first continuously curved diaphragm rolling and support surface and said piston rod having a generally discshaped guide member adjacent said piston and a rounded peripheral surface defining a second continuously curved diaphragm rolling and support surface; said continuously curved diaphragm rolling and support surfaces respectively engaging said pair of diaphragm curved rolling surfaces to support said diaphragm during reciprocation of said piston, whereby said diaphragm curved rolling surfaces roll along said continuously curved diaphragm rolling and support surfaces of the flange and guide member in opposite directions during reciprocation of the piston.

12. A pump as defined in claim 11 wherein said disk shaped guide member is located in predetermined relation with respect to said flange thereby to position said second diaphragm rolling and support surface at a level above said first rolling and support surface when said piston is in its top dead center position and at a level below said first diaphragm rolling and support surface when said piston is in its bottom dead center position, whereby said diaphragm rolls along said diaphragm rolling and support surfaces in opposite directions during reciprocation of said piston.

13. A pump as defined in claim 11 wherein said first valve means comprises a flap valve and said second valve means comprises a spring biased check valve.

14. A pump as defined in claim 11 wherein said means forming an eccentric rotary cam surface comprises an eccentric cam bushing mounted axially on said output shaft and a rotary bearing mounted on said cam bushing andhaving an outer annular surface engaged with said cam followers.

15. A pump as defined in claim 11 wherein said diaphragm cooperates with said piston to form a fluid chamber therebetween in said cylinder, and said cylinder has a fluid passage formed therein providing fluid communication between said fluid chamber and said suction port. 

1. A pump comprising, a cylinder defining a piston chamber, a piston located in said cylinder for reciprocation therein, a fluid manifold associated with said piston cylinder and having suction and discharge ports located in communication with said piston chamber, valve means operatively associated with said ports for simultaneously opening one of said ports and closing the other of said ports in response to the pressure in said piston chamber, means for hermetically sealing said piston chamber on the side of said piston opposite said ports, thereby to prevent loss of fluid in said pump through said piston chamber, and means for reciprocating said piston including a driven eccentric cam and a cam follower operatively connected between said piston and said cam, and means biasing said cam follower into engagement with said cam whereby rotation of said eccentric cam causes reciprocation of said piston in said chamber to alternately produce relatively low and high pressures in said chamber, thereby to draw fluid from said manifold through said suction port into said piston chamber and thence discharge said fluid through said discharge port; said means for hermetically sealing said piston chamber comprising a diaphragm formed of an elastomeric material operatively connected between said cylinder and said piston and having a first side facing said piston chamber and a second side opposite said first side and remote from said piston chamber; said diaphragm having inner and outer edge portions respectively connected to said piston and said cylinder and having a thickness between said inner and outer edge portions which is greater than the thickness of said edge portions thereby to form a bulge in said diaphragm between said edge portions to define a pair of curved rolling surfaces thereon; and means forming a pair of opposed continuously curved surfaces adjacent said second side of said diaphragm in predetermined relation to each other whereby said curved rolling surfaces of the diaphragm roll along said opposed continuously curved surfaces in opposite directions during reciprocation of said piston.
 2. A pump as defined in claim 1 wherein saiD piston includes a piston rod connected to said follower, and said means forming said opposed continuously curved surfaces includes a guide flange having a central bore opening towards said piston and piston chamber, said flange having a peripheral edge portion surrounding said bore, said edge portion being rounded to form one of said continuously curved surfaces, and a generally disk shaped guide member on said piston rod having a peripheral rounded surface forming the other of said continuously curved surfaces.
 3. A pump as defined in claim 2 wherein said diaphragm has a generally toroidal configuration when viewed in plan, said outer edge portion being clamped between said guide flange and said cylinder and said inner edge portion being clamped between said piston and said guide member thereby to form said bulge in said diaphragm between said inner and outer edge portions and form said curved rolling surfaces engaging the continuously curved surfaces of said flange and guide member.
 4. A pump as defined in claim 3 wherein said guide member is positioned to have its curved surface located at a level above the curved surface of said flange when said piston is in its top dead center position and at a level below the curved surface of said flange when said piston is in its bottom dead center position.
 5. A pump as defined in claim 2 wherein said means for biasing said cam follower into engagement with said cam comprises a compression spring operatively connected between said flange and said cam follower.
 6. A pump as defined in claim 2 wherein said valve means includes a flap valve operatively associated with said suction port.
 7. A pump as defined in claim 6 wherein said valve means further includes a check valve operatively associated with said discharge port for opening said discharge port when said flap valve closes said suction port.
 8. A pump as defined in claim 7 including an electric motor having an output shaft, and said eccentric cam comprises an eccentric cam bushing secured to said shaft and a rotary bearing mounted on said cam bushing in engagement with said cam follower.
 9. A pump as defined in claim 1 wherein said diaphragm cooperates with said piston to form a fluid chamber therebetween in said cylinder, and said cylinder has a fluid passage formed therein providing fluid communication between said fluid chamber and said suction port.
 10. The pump as defined in claim 3 wherein said continuously curved surfaces are spaced from each other and the bulge in said diaphragm enters the space between said continuously curved spaces thereby allowing said pump to withstand high pressures.
 11. A pump comprising, an electric motor having a rotary power output shaft, means forming an eccentric rotary cam surface mounted on said shaft, and a piston assembly operatively associated with said eccentric cam surface including a piston cylinder having a piston chamber formed therein, a piston located in said cylinder, having a piston rod and an operatively associated cam follower, a guide flange operatively connected to said cylinder between said cylinder and said cam and having a central bore opening towards said piston and piston chamber, said piston rod extending through said bore and being guided thereby during reciprocation of said piston, a compression spring operatively connected between said flange and said cam follower for biasing said cam follower into engagement with said cam surface whereby said piston is reciprocated during rotation of said cam surface to alternately produce relative low and high pressures in said cylinder, a fluid manifold operatively associated with said cylinder and having independent fluid inlet and outlet ports formed therein, anc communicating with said piston chamber, first valve means operatively associated with said inlet port for opening said inlet port and permitting fluid to flow into said piston chamber during the downward suction stroke of said piston and closing said inlet port on the upward-discharge stroke of said piston, and second valve means operatively associated with said outlet port for closing said outlet port on the downward-suction stroke of said piston, and opening said outlet port on the upward-discharge stroke of said piston, and a generally toroidally-shaped diaphragm formed of an elastomeric material operatively connected between said cylinder and said piston for hermetically sealing said piston chamber to prevent loss of fluid therefrom during operation of said pump; said diaphragm having a first side facing said piston chamber, a second side opposite said first side and remote from said piston chamber, inner and outer edge portions respectively connected to said piston and said cylinder, and a thickness between said inner and outer edge portions which is greater than the thickness of said edge portions, thereby to form a bulge in said diaphragm between said edge portions to define a pair of curved rolling surfaces thereon: said flange bore having a rounded upper peripheral edge portion adjacent said cylinder defining a first continuously curved diaphragm rolling and support surface and said piston rod having a generally disc-shaped guide member adjacent said piston and a rounded peripheral surface defining a second continuously curved diaphragm rolling and support surface; said continuously curved diaphragm rolling and support surfaces respectively engaging said pair of diaphragm curved rolling surfaces to support said diaphragm during reciprocation of said piston, whereby said diaphragm curved rolling surfaces roll along said continuously curved diaphragm rolling and support surfaces of the flange and guide member in opposite directions during reciprocation of the piston.
 12. A pump as defined in claim 11 wherein said disk shaped guide member is located in predetermined relation with respect to said flange thereby to position said second diaphragm rolling and support surface at a level above said first rolling and support surface when said piston is in its top dead center position and at a level below said first diaphragm rolling and support surface when said piston is in its bottom dead center position, whereby said diaphragm rolls along said diaphragm rolling and support surfaces in opposite directions during reciprocation of said piston.
 13. A pump as defined in claim 11 wherein said first valve means comprises a flap valve and said second valve means comprises a spring biased check valve.
 14. A pump as defined in claim 11 wherein said means forming an eccentric rotary cam surface comprises an eccentric cam bushing mounted axially on said output shaft and a rotary bearing mounted on said cam bushing and having an outer annular surface engaged with said cam followers.
 15. A pump as defined in claim 11 wherein said diaphragm cooperates with said piston to form a fluid chamber therebetween in said cylinder, and said cylinder has a fluid passage formed therein providing fluid communication between said fluid chamber and said suction port. 